Print systems usually apply recording material, like colorants, on a substrate or medium in the form of recording material like toner or ink according to a digitally defined, two-dimensional pattern of pixels with values that indicate a composition of these colorants. This pattern is generated out of a digital image, that may comprise objects in either vectorized or rasterized format, using conventional techniques like interpretation, rendering, and screening by a raster image processor. Depending on the intended print quality and the characteristics of the print process, the image pixels of the pattern may be printed in more than one pass, wherein a position on the substrate has an opportunity to receive recording material in one or more of the passes across the substrate. For every pass a pass image of image pixels to be printed may be derived.
As an extension of the applications of these systems, a print may be made by stacking recording material on top of each other. The effect of this stacking depends on the properties of the recording material. For example, a UV curable recording material or hot melt recording material will develop an elevation depending on the elevation value respectively a number of times an image pixel is printed. Elevation differences between various image pixels may create palpable differences between various parts of the print, giving the print a depth. Such prints are therefore termed 3D prints. An image pixel in a digital image that may lead to a 3D print, is not only characterized by a colour channel value, but additionally by the elevation channel value. The substrate may be a roll of print medium or a cut piece of print medium. The colour channel value is for example a CMYK channel, an RGB channel or a Black-and-White channel.
A category of printers that are used in 3D printing, is based on inkjet printing technology and uses recording material which is to be cured by radiation means, for example UV lamps. In these systems the objects are made by printing multiple amounts of recording material on top of each other in different passes. The different passes are derived from a design of the object resulting in a number of pass images. An object can for example consist of several thousands of passes. During printing of the passes the recording material is cured by means of the radiation means to solidify it. During printing the distance between the print head and the substrate has to be increased after each pass to create space for the growing object. Material is deposited on a substantially fixed distance from the print head to be able to deposit the drops of material accurately on the right place. Therefore all passes are substantially flat. This way of working results in a good exposure of the material to the radiation of the radiation means.
Due to many reasons, such as misdirecting nozzles in a print head, alignment errors and satellites from drops of material, it is possible that not all recording material is deposited on the right place. When recording material ends up in a place on the print that is insufficiently exposed to the radiations means, this material is expected to be insufficiently cured and solidified. Places at the print which are insufficiently exposed to the radiation means are for example holes or trenches in the print. Uncured recording material directed to pixels near a hole or trench may end up in the hole or the trench. In such a hole or trench the uncured recording material is prevented from sufficient exposure to the radiation means, for example when the distance between the bottom of the hole or the bottom of the trench and the print head and the radiation means increases due to the ongoing stacking of layers of recording material on the edges of the hole or trench. Uncured material may have a bad smell, may be unhealthy or toxic, may be soft, may be not hardened or may have a colour deviating from specifications for the print. These factors may lead to a lower value of the print or may result in a safety risk for anyone who comes into contact with the print.
It is an object of the invention to make prints which do not comprise uncured recording material in holes or trenches.